I have a relatively new series 7. It remains to be seen how it performs as the battery cycles hundreds of times.
edit: Fixed percent remaining. It was much better than I'd remembered.
I've considered getting one but hate the idea of having to charge my watch every day. My Pebble still gives me what I need, so I'm holding onto it for as long as the battery is in decent shape.
How long of a shower do you take? :-) A very related question is just how intensively will you use it. Here are some guidelines from Apple: https://www.apple.com/watch/battery/
My Series 6 watch is on my wrist for up to 23 hours a day. My battery is usually above 50% after a full day of use. I charge every day but for less than 30 minutes. (I usually take it off the charger before it is completely charged.)
Depending on your work and living arrangement (e.g. I'm mostly home) it's also so easy to drop onto the charger for just a few minutes. E.g. I can top-off the watch while I go into kitchen for a cup of coffee or a snack. So no need to devote a 30 minute continuous block of time.
I have low battery use because I mostly use the watch for notifications and activity tracking. I keep the display off by default (which is probably the main power draw).
The aluminum watch with sport loop is very light and comfortable. It's easy to forget you're wearing it.